Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

206
FXUS63 KLOT 252332
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
632 PM CDT Sat Apr 25 2026

.KEY MESSAGES...

- Severe thunderstorms Monday with all hazards possible, large
  hail, damaging winds and tornadoes. Heavy rain and localized
  flooding also possible.

- Potential for fog across primarily northeast Illinois late
  tonight into Sunday morning.

- Seasonable and dry conditions Sunday, but cooler temps near
  Lake Michigan.

&&

.DISCUSSION...
Issued at 249 PM CDT Sat Apr 25 2026

While this morning`s expansive stratus quickly eroded for a
vast majority of the area, a more prominent axis of status/fog
over Lake Michigan continues to advect onto the southern Lake
Michigan shore this afternoon. Satellite trends today combined
with the guidance that has best handled the stratus suggest that
stratus will redevelop/expand farther inland this evening and
overnight under a lowering, shallow and strong inversion. An
easterly veering low-level wind profile in response to high
pressure passing to the north should focus the stratus over
northeast Illinois, with less confidence on the western extent
before sunrise Sunday morning. While the lowering inversion has
the potential to erode cloud cover from top to bottom, it would
also result in very low ceilings that could transition to fog
late tonight into Sunday morning. Low stratus should then
quickly erode during the morning, though the stabilizing effect
of Lake Michigan may allow stratus to persist well into the
afternoon along the shore. Otherwise, temps Sunday will be
similar to today with highs in the lower 70s well inland to
around 50 near the shore.

Focus remains on a potentially significant severe weather event
in the region on Monday, with our forecast area remaining on
the eastern periphery of the greatest risk at this time.
Conceptually, the synoptic set-up with a negatively tilted
trough swinging across the Missouri River Valley, associated
surface low track across Iowa, and incoming strong mid/upper-
level jet dynamics all point to a concerning severe weather set-
up. The biggest questions for our area regarding both coverage
and intensity of convection revolve around 1) the amount of warm
sector contamination/longevity from any morning convection
associated with an incoming EML and 2) the potential convective
mode with eastward extent across the Mississippi River.

A low/mid-level wave tracking well ahead of the main trough
Monday morning will likely induce an area of elevated convection
fueled by steep mid-level lapse rates on the edge of the EML.
This convection will likely affect at least the northwest CWA,
with any stronger embedded cells capable of producing damaging
hail. There is remaining uncertainty with how far southeast this
convection extends into the remainder of the CWA, which could
delay erosion of existing inhibition while also focusing renewed
elevated convection on the north side of any effective outflow
boundary.

Conditional on a "clean" warm sector well northeast into
Illinois Monday afternoon, the noted strong forcing should erode
capping to the west and force discrete convection around the
I-35 corridor in Iowa and Missouri. Convection would likely
congeal with eastward extent across the Mississippi River,
favoring primarily a QLCS set-up late Monday afternoon and
especially Monday evening. ENE-pointed deep-layer shear vectors
suggest that convection could remain discrete or semi-discrete
through at least west-central Illinois, with any congealing line
likely containing supercell elements across much of the
remainder of Illinois. A narrowing higher theta-e axis with
northward extent may limit the supercell/QLCS tornado threat far
into northern Illinois, but the the embedded tornado threat
could also increase/expand in connection with increasing low-
level flow (60+ knot LLJ) during the early evening.

Will also need to monitor for a flooding threat, especially
north of I-88 where rivers levels remain elevated, if the
morning convection persists/redevelops through the day.

Behind Monday`s system, a transition to longwave troughing over
the eastern Great Lakes and eastern Ontario/Quebec will favor a
cooler end to April and start to May with perhaps a couple
chances for showers later in the week. Nighttime frost potential
will also increase late in the week, specifically for interior
northern Illinois.

Kluber

&&

.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 632 PM CDT Sat Apr 25 2026

Forecast concern for the terminals...

- Period of IFR to LIFR ceilings and fog late tonight into
  Sunday morning, especially at GYY.


A mid-level ridge (area of high pressure) continues to reside
overhead which is allowing mostly clear skies across much of
northern IL and northwest IN this evening. However, there is a
plume of low stratus and fog over southern Lake Michigan that
is oozing inland at GYY and MGC. Recent satellite trends do show
the back edge of this stratus and fog gradually eroding which
should allow the ceilings and visibilities at GYY to improve by
01z, but confidence is low as to whether or not the clouds will
fully scatter out. Regardless, the low clouds are forecast to
redevelop over Lower MI this evening and pivot westward
overnight as winds become more easterly. This should result in a
more widespread period of IFR and LIFR ceilings at all the TAF
sites after midnight through at least mid-morning on Sunday. In
addition to the low clouds, there is also a signal for some of
the low clouds to build down into fog as the inversion overhead
intensifies. While visibilities should generally be in the 3-5
SM range, some locally lower visibilities (as low as 1 mile) may
occur near the lake (15-20% chance).

Once the low clouds and fog erode Sunday morning, expect another
day of partly to mostly clear VFR skies. Winds will remain out
of the east around 10 kts with some occasional 15-20 kt gusts
possible during the afternoon.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 10 PM CDT this evening for the IL
     and IN nearshore waters.

&&

$$

Visit us at weather.gov/chicago